Radio receiving system



Dec. 10, 1935. R, RECHNITZERV Q 7 2,023,439

RADIO RECEIVING SYSTEM Filed June 13, 1932 INVENTOR RUDOLF RECHNITZER ATTORNEY Patented Dec. 10, 1935 UNITED STATES PATENT OFFICE RADIO RECEIVING SYSTEM tion of Germany Application June 13, 1932, Serial No. 616,858 In Germany June 10, 1931 8 Claims.

The present invention is broadly concerned with multi-range radio receivers.

It is an object of the present invention to adapt for use with a receiver arranged to tune to diiier ent frequency bands a volume control arrangement of the type wherein the volume is changed by varying the coupling between the source of energy and the amplifier and also by varying the bias on the amplifier tube.

In the drawing, Fig. 1 illustrates diagrammatically an embodiment of the invention applied to a system adapted to receive energy within different frequency ranges; and,

Fig. 2 is a diagrammatic illustration of a preferred embodiment of the invention.

In accordance with the invention, volume regulation is provided by means of a potentiometer resistance as shown at R2 Fig. 1. In this circuit, the amplifier tube V is coupled with a coil LA by way of a tuned circuit C. By a potentiometer tap, ground potential is applied at a. suitable point of resistor R2. The lower ends of the coil LA and the tuned circuit C are also connected to ground as shown. For the direct current insulation of the cathode of tube V, there is provided a. blocking condenser B. A further resistance device R1 is provided to act as a grid leak. Upon changing the potentiometer tap along the resistance device R2, two things take place, the damping of the antenna coil LA is varied, and the negative grid potential is varied by variation of the portion of the resistance R2 which is in series with the grid leak R1.

It has been found that the minimum value of R2 should at least be so fixed that for the lowest incoming frequency it will have approximately three times the value of the antenna impedance. When receiving Within the short wave length range (say between 200 and 600 meters) the antenna circuit is chosen so that its natural period will be about 900 meters. For a wave having a length of 200 meters, it will be seen that there re sults an antenna impedance of about 1000 ohms so that R2 should be about 3000 ohms. If such a receiver set is to be changed over to the long wave range, above 1000 meters, then referring to Fig. 1 the resistance device R2 connected in parallel to the antenna inductance must be increased in value in order that the shunt again may amount to about three times the antenna impedance. In order to provide uni-control when changing from one wave length to another, the condensers are not altered but only the inductance is altered so that the parallel damping resistance must be raised to a value which is three times higher.

In accordance with the usual formula describing resonant circuits, namely:

in order that the natural period of a circuit may be raised about five times as in the present instance, that is to say, from 250 meters to 1250 meters, in the presence of unvaried capacity, it will be necessary to increase the inductance about twenty-five times. As a result, the impedance of the antenna circuit must be increased five times. In proportion R2 must be raised, which in the case of the arrangement shown in Fig. 1 may be effected by disconnecting the resistance device R2 which is normally connected in parallel rela tionship to the potentiometer R2. In this manner, the relationship between parallel resistance and antenna impedance remains unchanged. The circuit arrangement described, involves the disadvantage that an additional switch must be provided for the disconnection of resistance device R2, and also the disadvantage that for long wave range operation the negative grid bias potential must be greatly increased. These disadvantages are obviated by the preferred embodiment of the invention by way of example in Fig. 2.

Briefly, in the arrangement shown in Fig. 2, in order to change over to another wave length, a part of the antenna inductance and also a part of the coil in the associated tuned circuit are short-circuited. It should benoted that the portions short-circuited have radio frequency potential at both ends thereof. In other words, the upper portions of the coils are short-circuited.

More specifically, in Fig. 2 the tube V may be considered a radio frequency amplifier tube having an input circuit C coupled to an antenna circuit. The input includes a parallel resonant circuit comprising a tuning condenser l and a coil. The coil is made up of two sections, 2 and 3. Short-circuiting switch 4 is provided in order that portion 2 of the coil may be short-circuited when desired, as when changing from one frequency band to another. The antenna is connected to ground through a coil which is made up of two sections 5 and 6. Coupling between the antenna and the tube input circuit is 'provided through the coils 5, 6 and 3, 2 as shown. Secticn 6 of the antenna coil may also be shortpircui ted by means of the switch 1. A point of the antenna coupling coil which is intermediate the two sections 5 and 6 is connected to the oathode of the tube through a resistor R2 and a resistor R1 in series. The antenna. end of the coil 6 is connected to the cathode side of the resistor R2 through a resistor Rz. By means of a variable tap 8, any point of the last named resistor may be connected to ground.

I claim:

1. In a radio receiver adapted to operate over a high-frequency band and over a low frequency band, an antenna circuit, an amplifier arrangement having input and output circuits, said amplifier arrangement including at least one electronic tube, means including inductance in the antenna circuit and the amplifier input circuit for coupling said antenna circuit and said amplifier input circuit, a frequency band changing control means comprising switches for both inductances and adapted to modify said inductances, modification of the antenna inductance also acting to change the antenna impedance, means for tuning said amplifier input circuit, a volume control arrangement for said receiver comprising a resistance network provided with means for controlling both the bias of the electronic tube of said amplifier and the degree of energy transfer between the antenna circuit and the amplifier input circuit, and means for maintaining the same relationship between the resistance of the network and the antenna impedance irrespective of the operation of said switches whereby substantially the same effects are obtained by said volume control when the receiver is operating at each range.

2. In a radio receiver adapted to operate over a, high frequency band and over a low frequency band, a primary circuit and a secondary circuit each thereof including inductance coupled together, said secondary circuit comprising an electronic tube provided with a tunable input circuit including the secondary inductance, said electronic tube being provided with an anode, a cathode and a control electrode, said tunable input circuit being connected between the control electrode and the cathode of said tube, switching means in the coupled circuits for modifying said primary and secondary inductances, means for connecting one end of the primary inductance to permit reception over different frequency bands to ground, a circuit for connecting the other end of the primary inductance to said cathode, said circuit including a pair of resistances in series, a direct current connection including a portion of said input circuit for connecting said grid electrode to ground, a variable tap operatively connected to one of said series resistances and ground, and a connection including a resistance element between a point intermediate said primary inductance and a point of said grid to cathode direct current path intermediate the two series resistances.

3. In a coupling arrangement between an antenna circuit and an amplifier said amplifier in- 'cluding an electronic tube provided with an anode, a cathode and a control electrode, said antenna circuit including a primary inductance coil, a secondary inductance coil connected between the control electrode and the cathode of the tube, said two coils being in coupled relationship whereby energy is transferred from the antenna circuit to the input of the electronic device, a tuning condenser connected across the secondary inductance coil for tuning said last named coil to any frequency within a certain band of frequencies, selective means cooperating with both the primary and secondary coils to alter the inductance of said coils for adapting said arrangement to tune to any frequency within another band of frequencies, means for controlling the amplification characteristics of said tube, means for controlling the signal input voltage applied thereto, a single means for operating both said control means, and means for maintaining substantially the same relationship between the antenna circuit impedance and said control means for all the different frequency bands to which the receiver may be adapted.

4. In a coupling arrangement for coupling a source of signal energy to an amplifier circuit said amplifier circuit including an electronic tube provided with an anode, a cathode and a control electrode, a primary coil connected across said source, a secondary coil in coupling relationship with said primary coil, said secondary coil being included in a connection between the control grid of said tube and the cathode thereof, a connection including a resistor from one end of the primary coil to said cathode, a connection from said control electrode to said cathode including said secondary coil and a portion of said resistance in series, a connection between said cathode and said control electrode including a second resistance at least a portion of the primary coil and at least a portion of the secondary coil in series, a

tuning device connected across the secondary coil for forming with said secondary coil a tuned circuit for tuning the input of said amplifier to any frequency within a predetermined band of frequencies and means for short-circuiting portions of both the primary and secondary coils for adapting said system to frequencies of another frequency range.

5. A radio receiver including a radio frequency amplifier adapted to operate over a high frequency band and over a low frequency band, said amplifier including an electronic tube having a tuned input circuit and an output circuit, means for controlling the amplification characteristics of said tube, a circuit including a source of signal energy coupled to said tuned input circuit and provided with means for changing the coupling relation between the source and the tuned input circuit so as to adapt the system for operation over a high frequency band and over a low frequency band, means for varying the coupling between the source and the tuned circuit to thereby control the amount of energy transferred from the source to said amplifier tube, said last named means and the means for controlling the amplification characteristic of the tube comprising a resistance network effectively in shunt with the source of signal energy and means for maintaining substantially the same relationship between the impedance of the source circuit and the resistance of said network for both the high and low frequency bands.

6. In a radio frequency coupling system adapted to operate over a plurality of widely different frequency bands said system including a primary winding and a secondary winding said two windings being in coupled relationship and operable means connected to both the primary and secondary windings acting upon operation in one direction to effect a substantial decrease in the inductance of both the primary and secondary windings, an electronic tube provided with an anode, a cathode and control electrode, a connection from one terminal of the primary winding to the cathode of said tube including a resistor, a connection from the other terminal of the primary winding to a variable tap on the resistor, a second resistor having one end connected to the cathode end of the first resistor and the other end connected to an intermediate point of the primary winding and means between said last named end of the second resistor and that terminal of the primary winding which is connected to the cathode of the tube and including said operable means for connecting the last named end of the second resistor to the last named terminal of the primary winding upon operation of said operable means to decrease the inductance of the primary winding whereby the second named resistor is, in effect, shunted directly across the first resistor, said two resistors being proporti'oned with respect to each other and the impedance of the primary inductance winding so that the impedance of the primary inductance winding is of the order of one-third the impedance of said resistors effectively shunted across the inductance Winding irrespective of changes in the inductance due to operation of the operable means.

7. In a radio frequency coupling system adapted to operate over a plurality of different frequency bands, said system including a primary inductance winding connected across a source of radio frequency energy and a coupled secondary inductance winding, an electronic tube provided. with an input circuit and an output circuit, said input circuit including the secondary winding and a variable tuning means, switching means connected with both the primary and secondary windings for, in effect, shunting out a portion of each winding so as to change the value of the inductance of both windings when changing the coupling system from one frequency band to another frequency band, means for controlling the signal input voltage applied to the input circuit of said tube including a variable by-pass impedance path related to the primary winding and arranged with respect thereto so as to effectively by-pass any desired portion of the radio frequency energy around said primary winding, means for controlling the amplification charac- -iliary resistor with respect to the first named bias teristics of the electronic tube comprising a variable bias resistor circuit connected in the tube input circuit, said bias resistor circuit and bypass path including a common portion, an operable common means for operating both said control means, means including an auxiliary bias resistor element connected in the tube input circuit and means controlled by said switching means'for varying the relationship of the auxresistor and the by-pass path for maintaining substantially the same relationship between both the variations in coupling and the variations in the amplification characteristics of the tube as a function of movements of the common control 1 means irrespective of changes of the system from one frequency band to another.

8. In a radio frequency coupling system, an antenna circuit including the primary winding of a transformer, an amplifier having an input cirg:

cuit and an output circuit, said input circuit including the secondary winding of said transformer, a direct current path for determining the amplification characteristics of the amplifier,

an alternating current path for determining the 2 degree of coupling between the antenna circuit and the amplifier, said two paths including a resistance network effectively in shunt with the antenna primary, said antenna primary being damped by the resistance network, means for si- 3 multaneously varying both the amplification factor of the amplifier and the energy transfer between the antenna circuit and the amplifier, selective means for modifying the primary and secondary windings of the transformer so as to adapt 3 the coupling system for frequencies of different ranges, means for operating said selective means and means controlled thereby for changing the effective resistance of the network across the antenna primary in such a way as to provide substantially the same damping effects across the antenna primary for all of the different frequency ranges while maintaining the direct current path unaltered.

RUDOLF RECHNITZER. 45 

